The broad objective of this research is to develop cost-effective technology for enhancing the rates of trichloroethene (TCE) biodegradation through bioremediation. The first aim will focus on selecting and optimizing electron donors for the purpose of enhancing the rates of anaerobic TCE degradation. Because the addition of growth substrates and electron donors can be site-specific, potential electron donors will be screened in laboratory studies for Aim 1 of this study. The gene clones developed for the project by Romine and Magnuson will be used to probe for the presence and expression pf TCE reductase in samples obtained for both laboratory and field studies. At some TCE concentrations that would confound attempts to monitor the fate of the injected TCE. Therefore, as part of Aim 2 of this study, we propose to overcome this limitation by using fluorinated hydrocarbons as surrogates for TCE. Laboratory studies will be conducted to identify appropriate fluorinated surrogates that can be used as surrogates for TCE in field tests. Standards of fluorinated surrogates as well as TCE will be provided to the Analytical Core in order to validate their alternative analytical methodology. Although field tests can be used to measure individual microbial respiratory process that are expressed by limited portions of the subsurface microflora, it is desirable to develop approaches that measure enzyme activities that are exhibited consistently by subsurface microorganisms, irrespective of any differences in their major metabolic or respiratory activities. The ability to estimate the size of the microbial population integrated during a push-pull test would provide important insights into the nature of the indigenous microbial community. To improve our ability to interpret in-situ rates of TCE degradation observed in field tests in Aim 3 we will develop and evaluate enzyme-substrate assays for estimating the metabolically-active microbial biomass interrogated during field tests. In Aim 3 we will implement these technologies for the purpose of determine the spatial and temporal variability of rates of anaerobic TCE degradation at TCE-contaminated field sites. In Aim 4 we will implement these technologies these technologies for the purpose of determining the spatial and temporal variability of rates of anaerobic TCE degradation at TCE- contaminated field sites and to determine the spatial and temporal variability in these other processes at the site scale. Information obtained from these field studies will be shared with the project by Thrall and Corely in order to support their risk assessment activities.